1. Technical Field
The present invention generally relates to dithiocarbamate derivatives and their use as multifunctional additives for lubricating oils and fuels.
2. Description of the Related Art
Automobile spark ignition and diesel engines have valve train systems, including valves, cams and rocker arms which present special lubrication concerns. It is extremely important that the lubricant, i.e., the engine oil, protects these parts from wear. It is also important for engine oils to suppress the production of deposits in the engines. Such deposits are produced from non-combustibles and incomplete combustion of hydrocarbon fuels (e.g., gasoline, diesel fuel oil) and by the deterioration of the engine oil employed. Accordingly, improving fuel economy is an important aspect of formulating an engine oil.
Zinc dialkyldithiophosphates (ZDDPs) have been used as antifatigue, antiwear, antioxidant, extreme pressure and friction modifying additives for lubricating oils for many years. However, they are subject to several drawbacks owing to their zinc and phosphorus contents. The presence of zinc contributes to the emission of particulates in the exhaust. In addition, during operation of an internal combustion engine, lubricating oil enters the combustion chambers by means such as clinging to cylinder walls as the piston makes its down stroke. When phosphorus-containing lubricating oil compositions enter the combustion reaction, phosphorus enters the exhaust stream where it acts as a catalyst poison thus shortening the useful life of the catalytic converter.
This is a major concern as effective catalytic converters are needed to reduce pollution and to meet governmental regulations designed to reduce toxic gases such as, for example, hydrocarbons, carbon monoxide and nitrogen oxides, in internal combustion engine exhaust emissions. Such catalytic converters generally use a combination of catalytic metals, e.g., platinum or variations, and metal oxides, and are installed in the exhaust streams, e.g., the exhaust pipes of automobiles, to convert the toxic gases to nontoxic gases. As previously mentioned, these catalyst components are poisoned by the phosphorous, or the phosphorous decomposition product of the zinc dialkyldithiophosphate; and accordingly, the use of engine oils containing phosphorous additives may substantially reduce the life and effectiveness of catalytic converters. Therefore, it would be desirable to reduce the phosphorous content in the engine oils so as to maintain the activity and extend the life of the catalytic converter.
There is also governmental and automotive industry pressure towards reducing the phosphorous content. For example, United States Military Standards MIL-L-46152E and the ILSAC Standards defined by the Japanese and United States Automobile Industry Association at present require the phosphorous content of engine oils to be at or below 0.10 wt. % with future phosphorous content being proposed to even lower levels. Accordingly, it would be desirable to replace or at least decrease the amount of zinc dialkyldithiophosphate in lubricating oils still further, thus reducing catalyst deactivation and hence increasing the life and effectiveness of catalytic converters while also meeting future industry standard proposed phosphorous contents in the engine oil.
However, simply decreasing the amount of zinc dialkyldithiophosphate presents problems because this may lower the antifatigue, antiwear, antioxidant, extreme pressure and friction modifying properties of the lubricating oil. Therefore, it is necessary to find a way to reduce the zinc and phosphorous content while still retaining antifatigue, antiwear, antioxidant, extreme pressure and friction modifying properties of the higher zinc and phosphorous content engine oils.
It would therefore be desirable to develop additives for lubricating oils that can improve the antifatigue, antiwear, antioxidant, extreme pressure and friction modifying properties of the oil while reducing the content of phosphorous of the lubricating oils.